Generally, a plasma display panel (PDP) has a disadvantage of large power consumption. A reduction of such power consumption requires enhancing a light-emitting efficiency and minimizing an unnecessary energy waste occurring in a driving process without a direct relation to a discharge.
An alternating current (AC)-type PDP coats an electrode with a dielectric material to use a surface discharge occurring at the surface of the dielectric material. In this AC-type PDP, a driving pulse has a high voltage of dozens to hundreds of volts (V) to make a sustaining discharge of tens of thousand to millions of cells, and has a frequency of more than hundreds of KHz. If such a driving pulse is applied to the cells, a charge/discharge having a high capacitance occurs.
When such a charge/discharge is generated at the PDP, a capacitive load of the panel does not cause an energy waste, but a lot of energy loss occurs at the PDP because a direct current (DC) power source is used to generate a driving pulse. Particularly, if an excessive current flows in the cell upon discharge, then an energy loss is increased. This energy loss causes a temperature rise of switching devices, which may break the switching devices in the worst case. In order to recover an energy generated unnecessarily within the panel, a driving circuit of the PDP includes an energy recovering circuit.
Referring to FIG. 1, an energy recovering circuit having been suggested by U.S. Pat. No. 5,081,400 of Weber includes first and second switches Sw1 and Sw2 connected, in parallel, between an inductor L and a capacitor Css, a third switch Sw3 for applying a sustaining voltage Vs to a panel capacitor Cp, and a fourth switch Sw4 for applying a ground voltage GND to the panel capacitor Cp.
First and second diodes D1 and D2 for limiting a reverse current are connected between the first and second switches Sw1 and Sw2. The panel capacitor Cp is an equivalent expression of a capacitance value of the panel, and reference numerals Re and R-Cp are equivalent expressions of parasitic resistances of an electrode and a cell provided at the panel, respectively. Each of the switches Sw1, Sw2, Sw3 and Sw4 is implemented by a semiconductor switching device, for example, a MOS FET device.
An operation of the energy recovering circuit shown in FIG. 1 will be described in conjunction with FIG. 2 assuming that a voltage equal to Vs/2 should be charged in the capacitor Css.
In FIG. 2, Vcp and Icp represent charge/discharge voltage and current of the panel capacitor Cp, respectively.
At a time t1, the first switch Sw1 is turned on. Then, a voltage stored in the capacitor Css is applied, via the first switch Sw1 and the first diode D1, to the inductor L. Since the inductor L constructs a serial LC resonance circuit along with the panel capacitor Cp, the panel capacitor Cp begins to be charged in a resonant waveform.
At a time t2, the first switch Sw1 is turned off while the third switch Sw3 is turned on. Then, a sustaining voltage Vs is applied, via the third switch Sw3, to the panel capacitor Cp. From the time t2 until a time t3, a voltage of the panel capacitor Cp remains at a sustaining level.
At a time t3, the third switch Sw3 is turned off while the second switch Sw2 is turned on. Then, a voltage of the panel capacitor Cp is recovered into the capacitor Css by way of the inductor L, the second diode D2 and the second switch Sw2.
At a time t4, the second switch Sw2 is turned off while the fourth switch Sw4 is turned on. Then, a voltage of the panel capacitor Cp drops into a ground voltage GND.
In the energy recovering circuit, there are requirements for improving the discharge characteristics of the panel, obtaining stable sustaining time, and increasing the efficiency of the energy recovered from the panel. For this, the conventional energy recovering circuit of FIG. 1 makes the inductance of the inductor L small to have it fast a rising time supplied to the panel. Thereby, the discharge characteristics can be increased and the inductance of the inductor L is made big such that the energy recovering efficiency can be improved.
However, because the conventional energy recovering circuit as in FIG. 1 uses the same inductor L on the charge/discharge path, if the rising time is made to be fast by setting the inductance of the inductor L to be small, the energy recovering efficiency decreases as it peak current becomes big. On the contrary, in the conventional energy recovering circuit, if the energy recovering efficiency is improved by setting the inductance of the inductor L to be big, because the rising time of the voltage supplied to the panel is lengthened, the discharge characteristics is deteriorated and it becomes difficult to obtain the sustaining time.
Also, because the conventional energy recovering circuit requires many semiconductor switching devices Sw1 to Sw4, an inductor L and a recovering capacitor for the operation of recovery, charge and sustaining steps, its manufacturing cost is high.